Description:
The accompanying geologic map (scale 1 :24,000) displays the structural and stratigraphic relationships of faulted homoclines of largely undated mid-Tertiary strata exposed over an area of ~250 km2 in the drainages of Camp Grant, Putnam, Dodson, and James Washes in uplands between the Santa Catalina and Tortilla Mountains west of the San Pedro trough. The dominantly homoclinal mid-Tertiary strata dip generally east-northeast, and are cut by normal faults dipping generally west-southwest. Previous maps of various parts of the study area at comparable scale (Krieger, 1968, 1974a, 1974b, 1974c; Hansen, 1983) were prepared without information now available about regional stratigraphic relationships (Dickinson, 1991). Most key geologic features were plotted correctly during previous mapping at smaller scale (Dickinson, 1987, sheets 3, 4, 6; 1988; 1991, figs. 1, 46; 1992), but the detailed placement of contacts and structures on the accompanying geologic map supersedes past mapping. In particular, an exposure of the Cloudburst Formation is delineated between James and Polecat Washes near the northern end of the map area, the position of the base of the Quiburis Formation along the western flank of the San Pedro trough is revised (from Dickinson, 1998, sheet 2) in the vicinity of Dodson and James Washes to the north of Elgin Wash, and transverse east-west faults (Cactus Hill and Putnam Wash faults) are mapped more completely and accurately than before.